The present invention relates to portable electronic equipment such as portable computers. More specifically, the present invention relates to dissipating heat that is generated by electronic devices within portable computers or other portable electronic equipment. For illustration purposes, this invention is described with reference to a portable computer.
Portable computers include various electronic devices that generate heat while the devices operate. For example, the central processing unit may generate eight to twelve watts, or more, and various other devices may generate a few watts per device. As a result, the devices may collectively generate twenty-five to thirty watts, or more.
Excess heat can damage electronic devices thereby shortening their lives. Accordingly, the portable computer industry has recognized a need to provide heat dissipation features in computers. It is well known to dissipate heat through the use of fans and heat pipes, for example.
In the prior art, heat pipes are fabricated separately from the chassis and such heat pipes are mechanically fastened to a chassis, as by screws, clips, or other fasteners, or by epoxy or by way of fixtures external to chassis members or bases. Accordingly, prior art heat pipes have a junction between the heat pipe and the chassis member that the heat pipe is attached to. This junction introduces thermal contact resistance, that is, it reduces heat conductivity at the junction making heat dissipation more difficult to achieve.
A heat pipe is a sealed vessel containing a working fluid and the vessel may be evacuated. Evacuation lowers the boiling point of the working fluid. In this specification, when the term xe2x80x9cevacuatedxe2x80x9d is used, it means evacuated to the extent necessary for lowing the boiling point of a working fluid to a desired temperature.
The vessel of a heat pipe has an evaporator section, an adiabatic section, and a condenser section and the vessel may contain a wick. In operation, electronic devices produce heat which is absorbed in the evaporator section of the heat pipe which causes evaporation into vapor of working fluid that is in the evaporator section. Working fluid in the form of vapor moves through the adiabatic section to the condenser section where it gives up its latent heat and condenses into fluid. A wick provides capillary action to provide return movement of fluid from the condenser section to the evaporator section.
Known wicks include fiber bundle wicks, mesh wicks, sintered wicks, grooved wicks, rough surface wicks, and others.
An example of use of heat pipes with magnesium or aluminum chassis members is disclosed in U.S. Pat. No. 5,973,920 to Altic, et al. A heat frame is formed from a piece of material such as magnesium or aluminum. A heat pipe carrier is provided in the frame as a location into which a heat pipe is mounted. The heat frame also features fins and a heat sink. While the Altic patent refers to a xe2x80x9cheat framexe2x80x9d the heat frame also provides mechanical support for the computer or for components of the computer and the heat frame it therefore functions as a chassis member in addition to its heat dissipating function.
U.S. Pat. No. 5,875,095 to Webb discloses an arrangement in which a heat sink structure forms a structural portion of a chassis of a computer. This arrangement features a channel and a heat pipe is disposed in the channel.
U.S. Pat. No. 5,884,693 to Austin et al. discloses an enclosure for housing electronics components in which a heat pipe is incorporated into the enclosure. The enclosure has a cabinet design with a hinged door which allows access to the components. This disclosure states that the material of the heat pipe may be for example, copper, gold, or aluminum. At the top of the enclosure an evaporator is located to receive heat that rises. A condenser is located at the bottom of the enclosure. The walls of the enclosure are hollow to provide passageways for fluid and vapor as they move between the evaporator and condenser. The enclosure is designed to be non-portable and buried in the earth at a fixed location.
Magnesium is a material that is commonly used to fabricate the chassis members of portable computers since this material is lightweight and since it provides a shield to reduce emission of radio frequency radiation from the computer. Plastics are also used to fabricate chassis members but plastics do not dissipate heat well. Aluminum may be used for chassis members but aluminum weighs more (is denser) than magnesium.
Magnesium has a density which is approximately seventy percent that of aluminum. However, the thermal conductivity of cast magnesium is about one-half that of cast aluminum. Accordingly, selection of magnesium instead of aluminum for a chassis member means that the savings in weight offered by magnesium is accompanied by a disadvantageous reduction in heat dissipation capacity of the magnesium chassis member.
It can be understood that a greater choice of alternative ways of providing heat dissipation means for protecting electronic equipment from damage caused by heat will be beneficial to the electronic industry. In particular, it can be seen that improvement in the heat dissipation capability of cast magnesium chassis members will be beneficial to the electronic industry. The present invention provides such alternative and improved means.
The invention provides a chassis member, which may be made of a cast or molded material such as magnesium, aluminum, or plastic, for mechanically supporting a heat producing electronic device in which the chassis member has a base and a cavity integral to the base. In a preferred embodiment, the cavity is a channel that is created by boring. The channel may be evacuated and the channel has an evaporator section, a condenser section, and a working fluid confined therein by a seal. The channel receives heat from an electronic device in an evaporator section of the channel and dissipates heat from the condenser section of the channel. In one embodiment a pedestal which may be an integral part of the chassis member provides for thermal coupling of heat from an electronic device to the evaporator section and a heat sink, such as a finned area, provides for thermal coupling of heat from the condenser area to the ambient air. Different types of wicks may be employed. In one embodiment, a completely fabricated heat pipe is inserted into the integrated channel. In another embodiment, the cavity is a matrix of channels which is provided integral to the chassis member. In other embodiments, the cavity has other shapes integral to the chassis member.